What happened
On May 30, 2015, a Schempp-Hirth Discus bT motor glider, registration JA20TD, was conducting navigation training near Takikawa Skypark in Hokkaido, Japan. The aircraft was launched via aerotow and released from the towing plane at an altitude of approximately 5,300 feet.
As the flight progressed, the aircraft's altitude fluctuated while navigating mountainous terrain. GPS records indicate that after crossing a ridge line toward the plains, the pilot likely attempted to restart the engine to regain altitude. During this process, the aircraft's altitude dropped significantly. At 12:36 JST, the glider crashed into a grassland in Urausu Town at an elevation of about 85 meters. The impact destroyed the aircraft, and the pilot was fatally injured.
The investigation
The Japan Transport Safety Board (JTSB) examined GPS flight data, aircraft wreckage, and meteorological records. The investigation focused on the aircraft's flight path, the performance of the sustainer-type engine, and the pilot's maneuvers during the descent. Investigators analyzed the aircraft's weight and balance, noting the center of gravity was estimated to be aft of the allowable range. The investigation also reviewed the operational characteristics of the motor glider, specifically the drag increase and altitude loss associated with extending the engine for a restart.
Findings
- The pilot attempted an off-field landing in a grassland without establishing a straight final approach course.
- The aircraft experienced a significant loss of altitude during a left turn at a low altitude.
- This loss of height may have been caused by the pilot maintaining a nose-up attitude during the turn, which reduced airspeed, or by a lack of coordinated turn control causing the aircraft to slip to the left.
- The decision to attempt an engine restart likely contributed to the altitude depletion, as the process of extending the engine and accelerating the propeller increases drag and reduces the glide ratio.